A work, e.g., semiconductor wafer, is polished by: pressing a surface of the work to be polished onto a surface of a polishing pad adhered on a polishing plate; and rotating the polishing plate with supplying slurry to the polishing pad.
After completing the polishing operation, the polishing pad includes produced dusts and slurry, so a polishing rate is lowered. Thus, high-pressure water is sprayed to the polishing pad, every time one batch of polishing operations are performed, so as to clean the polishing pad (see Japanese Laid-open Patent Publication No. 7-9340). Even if the polishing pad is cleaned every time one batch of polishing operations are performed, a surface of the polishing pad is deformed, in a wavelike fashion, with convex parts and concave parts, after about seven batches of polishing operations are performed. Therefore, flatness of the surface of the polishing pad is lowered, so a polishing rate must be lowered.
To solve the problem, for example, a work carrier is detached from a polishing apparatus and a dressing carrier is attached instead after performing about seven batches of polishing operations. Four ring-shaped flattening grind stones are respectively set in four through-holes of the dressing carrier, and polishing pads of an upper polishing plate and a lower polishing plate are ground by the flattening grind stones so as to flatten the surfaces of the polishing pads. Two of the four flattening grind stones grind the polishing pads of the lower polishing plate; the rest flattening grind stones grind the polishing pads of the upper polishing plate.
However, even if the polishing pads are cleaned, by spraying high-pressure water, after about seven batches of polishing operations are performed, convex parts and concave parts are gradually formed in the surfaces of the polishing pads while performing each batch of polishing operations. So, a polishing rate must be lowered. The polishing rate can be improved, by grinding the surfaces of the polishing pads with the flattening grind stones after seven batches of polishing operations are performed. However, the polishing rate is unstable. Thus, the polishing rate must be adjusted according to polishing time, so it is difficult to control polishing operations to polish works precisely. Further, it takes 15-20 minutes to attach the dressing carrier instead of the work carrier and dress the polishing pads after performing seven batches of polishing operations, so work efficiency must be lowered. Further, the surfaces of the polishing pads are ground, by the flattening grind stones, every time seven batches of polishing operations are performed, so spans of lives of the polishing pads must be shortened.